1. Field of the Invention
The present invention relates to a highly stable resin without the risk of bringing about undesired increase of the molecular weight or the viscosity in storage, use, or handling, such as a photo-curing resin with a good storage property, and a production method therefor.
Moreover, the present invention also relates to a hardenable resin composition containing a highly stable hardenable resin, capable of easily adjusting or evening the film thickness of a coated film without the risk of viscosity increase in storage or coating, and a production method therefor.
Furthermore, the present invention relates to a resin with excellent stability and transparency, a hardenable resin composition containing such a resin, and a production method therefor.
Still further, the present invention relates to a color filter and a liquid crystal panel with little color irregularity and contrast irregularity, with a protection film of a coloring layer and a spacer of a liquid crystal layer formed, using a highly stable hardenable resin composition, in particular, a photo-curing resin composition.
2. Description of the Related Art
Recently, as a flat display for a personal computer, color liquid crystal display devices have been propagated rapidly. As shown in FIG. 1, a color liquid crystal display device 101, in general, has a structure wherein a color filter 1 and an electrode substrate 2 such as a TFT substrate are faced with each other so as to provide a gap part 3 of about 1 to 10 μM, with a liquid crystal compound L filled in the gap part 3 and the periphery thereof sealed by a sealing member 4. The color filter 1 comprises a structure including a black matrix layer 6 formed in a predetermined pattern for blocking the light in the boundary part between the pixels, a coloring layer 7 with a plurality of colors (in general, three primary colors including red (R), green (G), and blue (B)) arranged in a predetermined order for forming each pixel or recently, a color filter, a protection film 8, and a transparent electrode film 9 successively laminated on a transparent substrate 5 in this order from the side close to the transparent substrate. Moreover, an alignment layer 10 is provided on the inner surface side of the color filter 1 and the electrode substrate 2 facing thereto. Furthermore, pearls 11 having a constant particle size are dispersed as a spacer in the gap part 3 for constantly and homogeneously maintaining the cell gap between the color filter 1 and the electrode substrate 2. A color image can be obtained by controlling the light transmittance of the pixels colored in each color or the liquid crystal layer behind the color filter.
The protection film 8 formed in the color filter serves for protecting the coloring layer and for flattening the color filter in the case a coloring layer is provided in the color filter. In a color liquid crystal display device, in the case the flatness of the transparent electrode film 9 is deteriorated due to existence of gap irregularity derived from the waviness on the surface of the transparent substrate of the color filter, gap irregularity among the R, G and B pixels, or gap irregularity within each pixel, color irregularity or contrast irregularity is generated so as to give rise to a problem of the image quality deterioration. Therefore, a high flatness is required to the protection film.
In the case the fine particle-like pearls 11 as shown in FIG. 1 are dispersed as the spacer, the pearls are dispersed randomly, independent from being behind the black matrix layer 6 or behind the pixels. In the case the pearls are disposed in the display area, that is, in the pixel part, a back lighting beam transmits the pearl part, and further, the orientation of the liquid crystal is disturbed in the vicinity of the pearls so that the display image grade is deteriorated remarkably. Then, as shown in FIG. 2, instead of dispersing the pearls, column-like spacers 12 having a height corresponding to the cell gap are formed on the inner surface side of the color filter in the area coinciding with the black matrix layer 6.
The above-mentioned protection film 8 and the column-like spacers 12 can be formed with a resin. In consideration of the adhesion property and the sealing property of the sealing part, the protection film 8 is preferably one capable of covering only the area of the transparent substrate with the coloring layer formed thereon. Moreover, the column-like spacers 12 need to be formed accurately in the area with the black matrix layer formed, that is, in the non-display area. Therefore, the protection film and the column-like spacers came to be formed with a photo-curing resin capable of easily limiting the area to be hardened by a photo mask.
Furthermore, in the case the surface applied with a photo-curing resin is developed with an organic solvent after exposure for forming the protection film or the column-like spacers, since handling and the waste liquid process are troublesome so that it is not satisfactory in terms of economy and stability, a photo-curing resin allowing an alkaline development after exposure has been developed by introducing an acidic group in a photo-curing resin.
As an alkaline-soluble photo-curing resin, for example, o-cresol novolak epoxy acrylate, or the like, having about 2,000 weight average molecular weight is known. The resin has a carboxylic acid group defining the alkaline solubility. However, since the resin uses a monomer component as an acryloyl group defining the curing property, the reliability in film formation is low. For example, it involves the risk of the residual monomer unit elution to the liquid crystal part. Furthermore, the film thickness may be reduced due to a large amount of the elution in the alkaline development.
Moreover, as a method for introducing a radical polymerizable group such as an acryloyl group into the molecular structure of a compound for providing the photo curing property, for example, a method of introducing a radical polymerizable group such as a methacryloyl group to an end by reacting of diols with excessive diisocyanate for preparing a reaction product with an isocyanate group remaining on the end, and reacting the isocyanate group of the reaction product with 2-hydroxyl ethylmethacrylate for producing urethane acrylate, is known. However, according to the method, as a principle, a (meth)acryloyl group can be introduced to only both ends of the molecular structure. Furthermore, although a method of radical polymerization by partially containing a compound having two or more radical polymerizable groups in a molecular such as a (meth)acryloyl group can be conceivable, the content of the radical polymerizable group cannot be controlled as well as a problem of gellation is also involved.
As mentioned above, although it is convenient to form the protection film and the column-like spacers of a color film with a photo-curing resin, it is difficult to control the amount of the alkaline soluble group such as a carboxyl group and the radical polymerizable group such as a (meth)acryloyl group according to the conventional photo-curing resin in consideration of the curing property and the alkaline solubility thereof.
According to the undisclosed knowledge obtained by the study of the present inventor, since the amount of the alkaline soluble carboxyl group and the radical polymerizable (meth)acryloyl group can be adjusted freely according to a copolymer resin having a principal chain comprising at least a component unit represented by the below-mentioned formula (1) and a component unit represented by the below-mentioned formula (2), with at least a part of the carboxyl group or the hydroxyl group thereof bonded with a (meth)acryloyloxy alkyl isocyanate compound represented by the below-mentioned formula (5) according to reaction of the isocyanate group of the compound, it is extremely suited as a photo-curing resin:

wherein R is hydrogen or an alkyl group having 1 to 5 carbon atoms, R1 is an alkylene group having 2 to 4 carbon atoms, R4 is an alkylene group, and R5 is hydrogen or methyl.
However, it is learned that in the case the above-mentioned copolymer resin is dissolved or dispersed in a solvent and left, the molecular amount is increased rapidly so as to raise the viscosity. According to our experiment, it is confirmed that the thickening phenomenon proceeds even in a room temperature, and proceeds more rapidly as the storage temperature is higher. Moreover, in an experiment utilizing the GPC (gel permeation chromatography), only by dissolving the above-mentioned copolymer resin in a solvent and leaving the same in a room temperature for two weeks, the molecular weight, which was 69,000 at the time of preparation, was increased to as much as 98,000, and the viscosity of the solution became 1.17 times. Furthermore, by storing the copolymer resin at 70° C. for three days, the molecular weight, which was 69,000 at the time of preparation, was increased to as much as 340,000, and the viscosity of the solution became 2.14 times. Moreover, it is also confirmed that the thickening phenomenon becomes further remarkable by mixing the copolymer resin with a thermosetting epoxy resin, an acrylic monomer, a polymerization initiator, or the like, dissolving in a solvent, and storing in the state of a coating liquid to be actually used.
Since the above-mentioned copolymer resin gives rise to such a thickening phenomenon, it is extremely troublesome in terms of storage, film thickness adjustment at the time of coating, maintenance of the homogeneity of the film thickness, or the like. That is, after once preparing a photo-curing resin composition coating liquid by dissolving the above-mentioned copolymer in a solvent and mixing with other materials, refrigeration storage is prerequisite and a long term storage is not possible. Moreover, even in the case thickening in storage can be avoided, since the coating operation is executed, in general, in a room temperature, the viscosity of the coating liquid rises rapidly during the operation of a day. Therefore, unless the viscosity of the coating liquid is checked frequently so as to modify the coating condition not only before starting the operation but also during the operation, the coated film thickness cannot be adjusted constantly. Furthermore, in the case the viscosity of the coating liquid rises too much, even if the coated film thickness can roughly be adjusted by modification of the coating condition, the coating irregularity cannot be avoided so that the film thickness homogeneity of the coated film cannot be maintained. Moreover, it is also difficult to reuse the remained portion of a coating liquid once used in a room temperature the other day, or to use the remained coating liquid with a new coating liquid added thereto.
In particular, the extremely high accuracy and homogeneity are required for the film thickness of the protection film for covering the coloring layer of the color film or the height of the column-like spacers for ensuring the cell gap. Compared with the protection film to be formed continuously in a collective area on the coloring layer, since the column-like spacers are formed intermittently according to the black matrix layer formation area by a height more than double as much as the height of the coloring layer, the size fluctuation can easily be brought about due to increase of the viscosity of the coating liquid. Moreover, in the case the coating resin came to have too high a molecular amount, the shape of the column-like spacers is deteriorated so that the strength as a spacer and other dynamic characteristics are deteriorated as well.
Therefore, in the case of forming a protection film or a column-like spacer of a color filter, in particular, of forming the column-like spacer, using a coating liquid of a photo-curing resin composition containing the above-mentioned copolymer resin, the thickening phenomenon of the coating liquid should be prohibited to a minimum level.
Furthermore, a good transparency is required to a resin for forming a coloring layer or a protection layer of a color film. However, according to the knowledge of the present inventors, the above-mentioned copolymer resin does not have a sufficient transparency.